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/*
* This library is part of OpenCms -
* the Open Source Content Management System
*
* Copyright (c) Alkacon Software GmbH & Co. KG (http://www.alkacon.com)
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* For further information about Alkacon Software, please see the
* company website: http://www.alkacon.com
*
* For further information about OpenCms, please see the
* project website: http://www.opencms.org
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
package org.opencms.ugc;
/**
* A queue used to enforce a certain wait time between requests for sessions for the same form configuration.
*/
public class CmsUgcSessionQueue {
/** True if the session queue is enabled. */
private boolean m_enabled;
/** The wait time between multiple session requests for the same configuration. */
private long m_interval;
/** The maximum number of threads waiting in the queue for the same configuration. */
private int m_maxLength;
/** The time at which the next thread should be scheduled to run. */
private long m_nextScheduleTime;
/** The number of threads waiting on this queue. */
private int m_waitCount;
/**
* Creates a new instance.
*
* @param enabled true if the queue should be enabled
* @param interval the wait time to use between multiple session requests
* @param maxLength the maximum length of the queue
*/
public CmsUgcSessionQueue(boolean enabled, long interval, int maxLength) {
m_enabled = enabled;
m_interval = interval;
m_maxLength = maxLength;
if (interval < 0) {
throw new IllegalArgumentException("Queue wait time must not be < 0");
}
if (maxLength < 0) {
throw new IllegalArgumentException("Queue maximum length must not be < 0");
}
}
/**
* Creates a session queue based on the given configuration.
*
* @param config the configuration for which to create the session queue
* @return the newly created session queue
*/
public static CmsUgcSessionQueue createQueue(CmsUgcConfiguration config) {
CmsUgcSessionQueue queue = new CmsUgcSessionQueue(
config.needsQueue(),
config.getQueueInterval().isPresent() ? config.getQueueInterval().get().longValue() : 0,
config.getMaxQueueLength().isPresent() ? config.getMaxQueueLength().get().intValue() : Integer.MAX_VALUE);
return queue;
}
/**
* Updates the queue parameters from the configuration object.
*
* @param config the form configuration
*/
public synchronized void updateFromConfiguration(CmsUgcConfiguration config) {
m_enabled = config.needsQueue();
m_interval = config.getQueueInterval().isPresent() ? config.getQueueInterval().get().longValue() : 0;
m_maxLength = config.getMaxQueueLength().isPresent()
? config.getMaxQueueLength().get().intValue()
: Integer.MAX_VALUE;
}
/**
* If there are currently any threads waiting on this queue, wait for the interval given on construction after the currenly last thread stops waiting.
*
* @return false if the queue was too long to wait, true otherwise
*/
public synchronized boolean waitForSlot() {
if (!m_enabled) {
return true;
} else {
long now = System.currentTimeMillis();
long timeToWait = m_nextScheduleTime - now;
if (timeToWait <= 0) {
// This happens either if this method is called for the first time,
// or if the wait interval for the last thread to enter the queue has
// already fully elapsed
m_nextScheduleTime = now + m_interval;
return true;
} else if (m_waitCount >= m_maxLength) {
return false;
} else {
m_nextScheduleTime = m_nextScheduleTime + m_interval;
m_waitCount += 1;
try {
// use wait here instead of sleep because it releases the object monitor
// note that timeToWait can't be 0 here, because this case is handled in the first if() branch,
// so wait() always returns after the given period
wait(timeToWait);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
m_waitCount -= 1;
return true;
}
}
}
}